Signal switches

nRF52840 DK Hardware

The nRF52840 DK has multiple analog switches that are used to connect and disconnect signals based on different scenarios.

Figure 1. Signal switches
TP3 TP2 TP4 TP1 SB51 SB53 SB50 SB52 NC1 1 IN 1-2 2 NO2 3 COM2 4 NC2 5 GND 6 NO3 7 COM3 8 NC3 9 IN 3-4 10 NO4 11 COM4 12 NC4 13 VCC 14 NO1 15 COM1 16 U6 FSA2466UMX C45 100nF VDD NC1 1 IN 1-2 2 NO2 3 COM2 4 NC2 5 GND 6 NO3 7 COM3 8 NC3 9 IN 3-4 10 NO4 11 COM4 12 NC4 13 VCC 14 NO1 15 COM1 16 U5 FSA2466UMX NC1 1 IN 1-2 2 NO2 3 COM2 4 NC2 5 GND 6 NO3 7 COM3 8 NC3 9 IN 3-4 10 NO4 11 COM4 12 NC4 13 VCC 14 NO1 15 COM1 16 U7 FSA2466UMX C42 100nF C48 100nF IF_OFF IF_OFF IF_OFF VDD VDD NC1 1 IN 1-2 2 NO2 3 COM2 4 NC2 5 GND 6 NO3 7 COM3 8 NC3 9 IN 3-4 10 NO4 11 COM4 12 NC4 13 VCC 14 NO1 15 COM1 16 U8 FSA2466UMX C50 100nF VDD SW7 VDD TRACE_SW UART_FC_OFF SW6 VDD SB46 SB45 SB42 SB43 SB44 nRF_ONLY BOOT/RESET IF_OFF R52 4k7 R53 4k7 SHIELD_DETECT VDD VDD IF_OFF R3 10k TP23 R4 10k TP21 TP20 BUTTONS SCL SDA I2C I2C TP5 TP6 TP7 SB54 SB55 SB57 SB56 TP8 SWDCLK SWDIO SWD3_RESET SWD3_SWO SWD3_IO SWD3_CLK CTS P0.05/AIN3 P0.08 P0.06 VCOM_RxD VCOM_TxD VCOM_RTS VCOM_CTS IF_OFF SW11 P0.11 P1.07 P0.12 P1.08 P0.24 P0.25 BTN2_OPT BTN2_DEF BTN1_OPT BTN1_DEF BUTTON3 BUTTON4 BUTTONS nRF52_UART RTS CTS_DEF CTS_OPT TxD RxD nRF52_UART P0.05/AIN3 P0.06 P0.07 P0.04/AIN2 P0.08 CTS SCL SDA USB_DETECT IMCU_BOOT RESET_PIN P0.18/RESET P0.18/RESET P0.18/RESET P1.00

The USB and SW6 control the signal switches by using the USB_DETECT signal as an input to SW6. The interface MCU can be disconnected either by unplugging the USB cable from J2 or by toggling the nRF ONLY switch SW6.

The signal controls switches U5, U6, and U7 that break the connection between the nRF52840 SoC and the interface MCU and control the power for the interface MCU. For more information, see Interface MCU power.

Switches U5 and U6 break the connection of the Universal Asynchronous Receiver/Transmitter (UART) lines and Serial Wire Debug (SWD)/RESET lines. Depending on user preference, the signal controls the routing of the RESET signal when the interface MCU is connected or disconnected as follows:

  • When the interface MCU is disconnected, cutting SB42 disconnects the RESET button (SW5) from the reset pin (P0.18) of nRF52840.
  • When the interface MCU is disconnected, shorting SB45 connects the RESET pin in the Arduino interface to the reset pin (P0.18) of nRF52840.
  • When the interface MCU is connected, shorting SB46 connects the RESET pin in the Arduino interface to the BOOT input of the interface MCU.
  • Shorting SB43 connects the RESET pin in the Arduino interface to the RESET button.
  • Shorting SB44 connects the RESET pin in the Arduino interface to the reset pin (P0.18) of nRF52840.

When a shield is connected, two analog switches connect the pull-up resistors to the SDA and SCL I2C bus lines. This function uses one ground pin on the Arduino shield to control the switch. This feature can be disabled by cutting SB33. To permanently enable pull-up resistors, short SB32.

Figure 2. Solder bridges: Shield detect and reset behavior
nRF52840 DK solder bridges: Shield detect and reset behavior

The last switch (U8) controls which GPIOs certain signals are routed to. This is due to some features using the same GPIOs as the Trace output by default. These analog switches are controlled by SW7. For more information, see Debug input and trace.